Fast Extended Shortwave Infrared Photodetector Using Silver Telluride Colloidal Quantum Dots

Extended shortwave infrared (eSWIR) photodetectors utilizing solution-processable semiconductors have attracted attention for applications such as ranging, night vision, and gas detection. In this context, colloidal quantum dots (CQDs) are promising materials due to their solution processability and easy bandgap tunability across visible to mid-infrared wavelengths. However, CQDs that absorb in the eSWIR region are predominantly composed of toxic elements, such as Hg and Pb, which violate RoHS regulations. Additionally, the need for cryogenic systems, along with slow response times, further limits the commercial viability of CQD-based eSWIR photodetectors. These challenges have led to the development of new, non-toxic CQDs for eSWIR photodetectors.

In this study, we fabricated a novel eSWIR photodetector using silver telluride (Ag₂Te) CQDs. Ag₂Te CQDs are RoHS-compliant and possess a smaller effective mass compared to II-V and III-V CQDs, enabling fast response times. Given the intricate crystallographic structure of monoclinic Ag₂Te CQDs, we carefully designated thiol ligands to enable efficient ligand exchange, which results in reduced trap density and improved carrier mobility. Furthermore, a vertical p-n photodiode with a favorable energy-level landscape is employed to facilitate charge extraction, leading to a fast, room-temperature-operable, and toxic-element-free CQD photodetector. As a result, the best-performing photodetector demonstrated a fall time of 72 ns at 298 K, representing the fastest response time among all prior CQD-based eSWIR photodetectors, including those containing toxic elements.